Background: The precise determination of the Ft value in T=1/2 mixed mirror decays is an important avenue for testing the standard model of the electroweak interaction through the determination of Vud in nuclear β decays. C11 is an interesting case, as its low mass and small QEC value make it particularly sensitive to violations of the conserved vector current hypothesis. The present dominant source of uncertainty in the C11Ft value is the half-life. Purpose: A high-precision measurement of the C11 half-life was performed, and a new world average half-life was calculated. Method: C11 was created by transfer reactions and separated using the TwinSol facility at the Nuclear Science Laboratory at the University of Notre Dame. It was then implanted into a tantalum foil, and β counting was used to determine the half-life. Results: The new half-life, t1/2=1220.27(26) s, is consistent with the previous values but significantly more precise. A new world average was calculated, t1/2world=1220.41(32) s, and a new estimate for the Gamow-Teller to Fermi mixing ratio ρ is presented along with standard model correlation parameters. Conclusions: The new C11 world average half-life allows the calculation of a Ftmirror value that is now the most precise value for all superallowed mixed mirror transitions. This gives a strong impetus for an experimental determination of ρ, to allow for the determination of Vud from this decay.< Leer menos